System, method and apparatus for hardfacing composition for earth boring bits in highly abrasive wear conditions using metal matrix materials

ABSTRACT

A highly abrasive wear metal matrix composite hardfacing material for downhole tools is disclosed. The hardfacing material may comprise a matrix of a softer material with high hardness, such as amorphous nanocomposite steel alloys, and one or more hard component materials. The hard component materials may comprise sintered tungsten carbide, monocrystalline WC, polycrystalline WC, and the additional component of spherical cast tungsten carbide. Alternatively, a matrix of softer material, hard component materials and crushed cast tungsten carbide may be used.

This non-provisional patent application claims priority to and the benefit of U.S. Provisional Patent App. No. 60/871,270, which was filed on Dec. 21, 2006.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in general to hardfacing and, in particular, to an improved highly abrasive wear metal matrix composite hardfacing materials, such as for downhole tools.

2. Description of the Related Art

It is a long-standing practice in the design and manufacture of earth-boring bits to apply wear-resistant hardfacing materials to the surfaces of such bits that are subjected to abrasive wear during drilling operations. In earth-boring bits of the rolling cutter variety, these surfaces include the teeth of bits of the milled or steel tooth variety, the gage surfaces of the rolling cutters and the shirttails of the bit legs comprising the bit body.

In the past, these hardfacing compositions generally comprise carbides of the elements of Groups IVB, VB and VIB in a matrix metal of iron, cobalt or nickel and alloys and mixtures thereof. The hardfacing is applied by melting the matrix and a portion of the surface to which the hardfacing is applied with an oxyacetylene or atomic hydrogen torch. The carbide particles give the hardfacing material hardness and wear resistance, while the matrix metal lends the hardfacing fracture toughness. A hardfacing composition must strike an adequate balance between wear resistance (hardness) and fracture toughness. A hardfacing composition that is extremely hard and wear-resistant may lack fracture toughness, causing the hardfacing to crack and flake prematurely. Conversely, a hardfacing with adequate fracture toughness, but inadequate hardness and wear resistance, is eroded prematurely and fails to serve its purpose.

Many factors affect the suitability of a hardfacing composition for a particular application. These factors include the chemical composition and physical structure of the carbides employed in the composition, the chemical composition and microstructure of the matrix metal or alloy, and the relative proportions of the carbide materials to one another and to the matrix metal or alloy.

One early advance in hardfacing compositions for use in earth-boring bits is disclosed in commonly assigned U.S. Pat. No. 3,800,891, to White. This patent discloses a hardfacing composition comprising sintered tungsten carbide in an alloy steel matrix. Sintered tungsten carbide comprises grains or particles of tungsten carbide sintered with and held together by a binder of non-carbide material, such as cobalt. The sintered tungsten carbide possesses greater fracture toughness than the more conventional cast tungsten carbide, such that the resulting hardfacing composition possess good fracture toughness without sacrificing hardness and wear resistance.

U.S. Pat. No. 4,836,307, to Keshavan, discloses a hardfacing composition employing particles of cemented or sintered tungsten carbide and relatively small particles of single crystal monotungsten carbide, sometimes referred to as “macrocrystalline” tungsten carbide, in a mild steel matrix. This composition purports to possess the advantages of sintered tungsten carbide, as disclosed in U.S. Pat. No. 3,800,891, with the advantages of single crystal monotungsten carbide, which is harder than the cemented or sintered tungsten carbide, yet is less brittle than the alternative cast carbide.

U.S. Pat. No. 5,089,182, to Findeisen, discloses a method of manufacturing cast carbide pellets that are generally spherical in shape and have improved mechanical and metallurgical properties over prior-art carbide pellets. These cast pellets are not truly spherical, but are sufficiently symmetrical that residual stresses in the pellets are minimized. Also, the generally spherical shape of these pellets eliminates corners, sharp edges and angular projections, which are present in conventional crushed particles, that increase residual stresses in the particles and tend to melt as the hardfacing composition is applied to the surface.

U.S. Pat. No. 5,663,512, to Schader, discloses a hardfacing composition which includes a quantity of spherical sintered tungsten carbide granules and a quantity of cast spherical cast tungsten carbide granules in a eutectic form of WC/W₂C. During application, some melting of the sintered spherical carbide granules occurs, which precipitates into the metal matrix and coats the spherical WC/W₂C granules. Although this composition provides a good balance between hardness and fractures toughness, a drill bit having the toughness, ductility, and impact strength of steel and the hardness and wear resistance of tungsten carbide or other hard metal on the exterior surface, but without the problems of prior art steel body or steel tooth bits would be desirable.

SUMMARY OF THE INVENTION

Embodiments of a system, method, and apparatus for a highly abrasive wear metal matrix composite hardfacing material for downhole tools are disclosed. The hardfacing material may comprise a matrix of relatively softer material with high hardness, such as amorphous nanocomposite steel alloys, and one or more hard component materials. The hard component materials may comprise sintered tungsten carbide (e.g., WC/Co), monocrystalline WC, multicrystalline or polycrystalline WC, and the additional component of spherical cast tungsten carbide (e.g., a eutectic of WC/W₂C). Alternatively, a matrix of softer material, hard component materials and crushed cast tungsten carbide may be used.

The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of the present invention, which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings which form a part of this specification. It is to be noted, however, that the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.

FIG. 1 is an isometric view of one embodiment of a bit constructed in accordance with the present invention;

FIG. 2 is a micrograph illustration of one embodiment of hardfacing material constructed in accordance with the invention; and

FIG. 3 is a micrograph illustration of another embodiment of hardfacing material constructed in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Hardfacing materials formed from amorphous nanocomposite steel alloys, such as NANOSTEEL®, such as those now commercially available for plasma transferred arc (PTA) welding applications. Some recent materials are reported to have high hardness while retaining their toughness, which is desirable for impact loading.

One of the problems associated with conventional PTA nickel-based or iron-based hardfacing materials is that their retention of the hard component particles is compromised as the hardness of the softer material is increased. This may produce an embrittled deposit and compromise the hardfacing. However, as a result of improved application techniques, more exotic materials such as amorphous nanocomposite steel alloys may be utilized as a relatively softer material in conjunction with hard component materials on downhole tools.

For example, sintered tungsten carbide or cast tungsten carbide, e.g., spherical or crushed, monocrystalline or polycrystalline WC, or other carbide formers may be used as the hard component materials in the softer amorphous nanocomposite steel alloys to achieve even better wear resistance without losing toughness or compromising the end deposit. By varying the physical sizes and combinations of these hard component materials, especially spherical sintered tungsten carbide pellets and/or spherical cast tungsten carbide, superior wear resistant compositions are achieved.

Referring now to FIG. 1, one embodiment of a highly abrasive wear metal matrix composite hardfacing material 21 is shown. The invention is particularly well suited for use at many different locations on downhole tools, such as on the roller cone legs of a drill bit 23 or other types of downhole tools (e.g., steel tooth bits, TCI bits, steel body PDC bits, RWD tools, etc.) but it is not limited to these applications.

As shown in FIG. 2, the hardfacing material may comprise a matrix 11 of a softer material with high hardness (e.g., a minimum of 60 Rc, and in some embodiments, 65+ Rc, e.g., 72 Rc) such as amorphous nanocomposite steel alloys (e.g., NANOSTEEL®) and one or more hard component materials. The hard component materials may be selected from, for example, sintered tungsten carbide (e.g., WC/Co) (spherical 13 or crushed 15), monocrystalline WC, macrocrystalline WC, multicrystal or polycrystalline WC and, in some embodiments, the additional component of spherical cast tungsten carbide (e.g., a eutectic of WC/W₂C) 17, each of which may be crushed in form. Another example is shown in FIG. 3, having a matrix 31 of relatively softer material (e.g., amorphous nanocomposite steel alloy) and hard component materials such as monocrystalline WC 33 and crushed cast tungsten carbide 35.

The invention may comprise numerous different size ratios between the various components. For example, the particle size for each component may range from, for example, mesh −16 to +325. In addition, the distribution between the components also may be formulated in weight percentages as, for example, 30 wt % soft component and 70 wt % hard component. The range for other embodiments comprises a soft component low end of about 20 wt % to a soft component high end of 90%, with complementary hard component low and high ends at 10 wt % and 80 wt %. Moreover, the hard component may comprise up to 100% sintered tungsten carbide (e.g., crushed or spherical), or less than 100% spherical cast tungsten carbide (e.g., crushed), or mono-, macro- or polycrystalline WC, or any combination thereof.

While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, although the invention is described with PTA welding, other welding techniques known to those skilled in the art, such as MIG, TIG (any of preceding may be continuous or pulsed arc applications), Flamespray, oxyacetylene, etc., also may be used. 

1. A hardfacing material formed from a metal matrix composite for highly abrasive wear applications, comprising: a matrix formed from a softer amorphous nanocomposite steel alloy and having a hardness of at least 60 Rc; and a hard component in the matrix of softer amorphous nanocomposite steel alloy, the hard component having a higher hardness than the matrix.
 2. A hardfacing material according to claim 1, wherein the matrix comprises a range of about 20 to 90 wt % of the metal matrix composite, and the hard component comprises a range of about 10 to 80 wt % of the metal matrix composite.
 3. A hardfacing material according to claim 1, wherein the matrix comprises about 30 wt % of the metal matrix composite, and the hard component comprises about 70 wt % of the metal matrix composite.
 4. A hardfacing material according to claim 1, wherein the matrix comprises about 40 wt % of the metal matrix composite, and the hard component comprises about 60 wt % of the metal matrix composite.
 5. A hardfacing material according to claim 1, wherein the hard component comprises spherical sintered tungsten carbide pellets.
 6. A hardfacing material according to claim 1, wherein the hard component is formed from at least one of sintered tungsten carbide and cast tungsten carbide.
 7. A hardfacing material according to claim 1, wherein the hard component is formed from at least one of spherical and crushed tungsten carbide.
 8. A hardfacing material according to claim 1, wherein the hard component is formed from at least one of monocrystalline WC, macrocrystalline WC and polycrystalline WC.
 9. A hardfacing material according to claim 1, wherein the hard component further comprises spherical cast tungsten carbide.
 10. A hardfacing material according to claim 1, wherein the hard component has a particle size in a mesh range of −16 to +325, and the matrix has a hardness of at least 65 Rc.
 11. A downhole tool, comprising: a downhole tool body; a hardfacing on the downhole tool body, the hardfacing being formed from a metal matrix composite for highly abrasive wear applications; the hardfacing comprising: a matrix formed from a softer amorphous nanocomposite steel alloy and having a hardness of at least 60 Rc; and a hard component in the matrix of softer amorphous nanocomposite steel alloy, the hard component having a higher hardness than the matrix.
 12. A downhole tool according to claim 11, wherein the matrix comprises a range of about 20 to 90 wt % of the metal matrix composite, and the hard component comprises a range of about 10 to 80 wt % of the metal matrix composite.
 13. A downhole tool according to claim 11, wherein the downhole tool body comprises a drill bit body having gage areas, legs, and roller cones rotatably mounted to the legs, and each of the roller cones having steel teeth extending therefrom, and wherein the hardfacing is located on at least one of the gage areas, legs, and steel teeth.
 14. A downhole tool according to claim 11, wherein the matrix comprises about 40 wt % of the metal matrix composite, and the hard component comprises about 60 wt % of the metal matrix composite.
 15. A downhole tool according to claim 11, wherein the hard component comprises spherical sintered tungsten carbide pellets.
 16. A downhole tool according to claim 11, wherein the hard component is formed from at least one of sintered tungsten carbide and cast tungsten carbide.
 17. A downhole tool according to claim 16, wherein the hard component further comprises at least one of spherical and crushed tungsten carbide.
 18. A downhole tool according to claim 16, wherein the hard component further comprises at least one of monocrystalline WC, macrocrystalline WC and polycrystalline WC.
 19. A downhole tool according to claim 11, wherein the hard component further comprises spherical cast tungsten carbide.
 20. A downhole tool according to claim 11, wherein the hard component has a particle size in a mesh range of −16 to +325, and the matrix has a hardness of at least 65 Rc.
 21. A method of forming a drill bit, comprising: (a) providing roller cones with steel teeth extending therefrom; (b) applying a hardfacing on the steel teeth, the hardfacing being formed from a metal matrix composite for highly abrasive wear applications; the hardfacing comprising a matrix formed from a softer amorphous nanocomposite steel alloy and having a hardness of at least 60 Rc, and a hard component in the matrix of softer amorphous nanocomposite steel alloy, the hard component having a higher hardness than the matrix; and (c) rotatably mounting the roller cones to a drill bit body.
 22. A method according to claim 21, wherein step (b) comprises applying the hardfacing to the steel teeth with a welding technique selected from the group consisting of PTA pulsed arc, PTA continuous arc, MIG pulsed arc, MIG continuous arc, TIG pulsed arc, TIG continuous arc, and oxy-acetylene.
 23. A method according to claim 21, wherein the matrix comprises a range of about 20 to 90 wt % of the metal matrix composite, and the hard component comprises a range of about 10 to 80 wt % of the metal matrix composite.
 24. A method according to claim 21, wherein the hard component is selected from the group consisting of sintered tungsten carbide, cast tungsten carbide, spherical sintered tungsten carbide pellets, spherical tungsten carbide, crushed tungsten carbide, monocrystalline WC, macrocrystalline WC and polycrystalline WC.
 25. A method according to claim 21, wherein the hard component further comprises spherical cast tungsten carbide, and the hard component has a particle size in a mesh range of −16 to +325, and the matrix has a hardness of at least 65 Rc. 